Quantum dots (qdots or QDs) are currently being studied as phosphors in solid state lighting (SSL) applications (LEDs). They have several advantages such as a tunable emission and a narrow emission band which can help to significantly increase the efficacy of LED based lamps, especially at high CRI. Typically, qdots are supplied in an organic liquid, with the quantum dots surrounded by organic ligands, such as oleate (the anion of oleic acid), which helps to improve the emission efficiency of the dots as well as stabilize them in organic media.
The synthesis of silica coatings on quantum dots is known in the art. Koole et al. (in R. Koole, M. van Schooneveld, J. Hilhorst, C. de Mello Donegá, D.'t Hart, A. van Blaaderen, D. Vanmaekelbergh and A. Meijerink, Chem. Mater., 20, p. 2503-2512, 2008) describe experimental evidence in favor of a proposed incorporation mechanism of hydrophobic semiconductor nanocrystals (or quantum dots, QDs) in monodisperse silica spheres (diameter ˜35 nm) by a water-in-oil (W/O) reverse microemulsion synthesis. Fluorescence spectroscopy is used to investigate the rapid ligand exchange that takes place at the QD surface upon addition of the various synthesis reactants. It was theorized that hydrolyzed TEOS has a high affinity for the QD surface and replaces the hydrophobic amine ligands, which enables the transfer of the QDs to the hydrophilic interior of the micelles where silica growth takes place. By hindering the ligand exchange using stronger binding thiol ligands, the position of the incorporated QDs could be controlled from centered to off-center and eventually to the surface of the silica spheres. They were able to make QD/silica particles with an unprecedented quantum efficiency of 35%.
WO2013/057702 describes a luminescent nano particles based luminescent material comprising a matrix of interconnected coated luminescent nano particles, wherein for instance wherein the luminescent nano particles comprise CdSe, wherein the luminescent nano particles comprise a coating of CdS and wherein the matrix comprises a coating comprising ZnS. The luminescent material according may have a quantum efficiency of at least 80% at 25° C., and having a quench of quantum efficiency of at maximum 20% at 100° C. compared to the quantum efficiency at 25° C.
WO2005/107818 describes fluorescent, radio-opaque and magnetic quantum nanoparticles, useful as multifunctional contrast agents or probes for in vivo bio imaging, and methods of their use. The document describes the use for multifaceted bio imaging (e.g., intra-arterial pre-operative brain mapping and broad based in vivo diagnostic imaging), including imaging of various cell types, such as stem cells.
WO2009/046392 describes methods for preparing rare earth doped monodisperse, hexagonal phase upconverting nanophosphors, the steps of which include: dissolving one or more rare earth precursor compounds and one or more host metal fluoride compounds in a solvent containing a tri-substituted phosphine or a tri-substituted phosphine oxide to form a solution; heating the solution to a temperature above about 250° C. at which the phosphine or phosphine oxide remains liquid and does not decompose; and precipitating and isolating from the solution phosphorescent hexagonal phase monodisperse nanoparticles of the host metal compound doped with one or more rare earth elements. Nanoparticles and methods for coating rare earth doped upconverting nanophosphors with SiO2 are also described.